U.S. patent number 8,319,960 [Application Number 12/770,337] was granted by the patent office on 2012-11-27 for defect inspection system.
This patent grant is currently assigned to Hitachi High-Technologies Corporation. Invention is credited to Kenji Aiko, Shuichi Chikamatsu, Hisafumi Iwata, Minori Noguchi.
United States Patent |
8,319,960 |
Aiko , et al. |
November 27, 2012 |
Defect inspection system
Abstract
A defect inspection system can suppress an effect of light from
a sample rough surface or a regular circuit pattern and increasing
a gain of light from a defect such as a foreign material to detect
the defect on the sample surface with high sensitivity. When a lens
with a large NA value is used, the outer diameter of the lens is
10a, and an angle between the sample surface and a traveling
direction of the light from a defect is .alpha.1. An oblique
detection optics system receives the light from the defect at a
reduced elevation angle .alpha.2 with respect to the sample surface
to reduce light from the sample rough surface, an oxide film rough
bottom surface, and a circuit pattern, and to increase the amount
of the light from the defect and detected. The diameter 10a of a
lens is smaller than the diameter 10b, resulting in a reduction in
the ability to focus the scattered light. When a lens with an outer
diameter 10c is used to improve the focus ability, the lens
interferes with the sample. To avoid the interference, a portion of
the lens interfering with the sample is removed. The lens has an
aperture larger than the diameter 10b while the lens receives the
light scattered at the elevation angle .alpha.2, making it possible
to improve the ability to detect defects and lens performance
simultaneously.
Inventors: |
Aiko; Kenji (Hitachinaka,
JP), Chikamatsu; Shuichi (Kounosu, JP),
Noguchi; Minori (Joso, JP), Iwata; Hisafumi
(Hayama, JP) |
Assignee: |
Hitachi High-Technologies
Corporation (Tokyo, JP)
|
Family
ID: |
39984366 |
Appl.
No.: |
12/770,337 |
Filed: |
April 29, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100271473 A1 |
Oct 28, 2010 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
12081107 |
Apr 10, 2008 |
7733474 |
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Apr 13, 2007 [JP] |
|
|
2007-106082 |
|
Current U.S.
Class: |
356/237.2;
356/237.5 |
Current CPC
Class: |
G01N
21/9501 (20130101); H04N 7/18 (20130101); G01N
2021/8822 (20130101); H01L 22/12 (20130101); G01N
21/956 (20130101); H01L 2924/0002 (20130101); H01L
2924/0002 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
G01N
21/88 (20060101) |
Field of
Search: |
;356/237.1-237.5,337 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
01-265220 |
|
Oct 1989 |
|
JP |
|
2004-093252 |
|
Mar 2004 |
|
JP |
|
2004-177284 |
|
Jun 2004 |
|
JP |
|
3566589 |
|
Jun 2004 |
|
JP |
|
2005-156537 |
|
Jun 2005 |
|
JP |
|
2005-283190 |
|
Oct 2005 |
|
JP |
|
2006-017630 |
|
Jan 2006 |
|
JP |
|
2006-098154 |
|
Apr 2006 |
|
JP |
|
2006-162500 |
|
Jun 2006 |
|
JP |
|
2006-201179 |
|
Aug 2006 |
|
JP |
|
2007-302997 |
|
Nov 2007 |
|
JP |
|
Other References
English translation of Japanese Office Action and abstracts of
references cited therein, issued in Japanese Patent Application No.
2007-106082, dated Jul. 26, 2011. cited by other.
|
Primary Examiner: Pham; Hoa
Attorney, Agent or Firm: McDermott Will & Emery LLP
Parent Case Text
RELATED APPLICATIONS
This application is a Continuation of U.S. application Ser. No.
12/081,107, filed on Apr. 10, 2008, now U.S. Pat. No. 7,733,474
claiming priority of Japanese Patent Application No. 2007-106082,
filed on Apr. 13, 2007, the entire contents of each of which are
hereby incorporated by reference.
Claims
What is claimed is:
1. An inspection apparatus for detecting a defect of an object
comprising: an irradiation system which irradiates the object with
light; a detection system which accumulates light from the object,
said detection system including an aberration correction system
configured to correct aberration of said light from said object,
wherein said aberration correction system comprises a plurality of
lenses lining up in a direction including an axis of said lenses so
as to correct aberration of light acquired by said system, wherein
said lenses have substantially elliptical shapes, each of said
elliptical shapes including a first side and a second side facing
each other, and two elliptical arcs facing each other, wherein at
least one of said first side and said second side is substantially
straight, and a distance between said first side and said second
side is smaller than a distance between said two elliptical arcs,
wherein said detection system includes a sensor for detecting light
corrected by said aberration correction system, and wherein said
detection system includes an objective lens, said objective lens
being arranged between a mounting position of said object substrate
and said aberration correction system, wherein said objective lens
has substantially elliptical shapes, each of said elliptical shapes
including a third side and a fourth side facing each other, and two
elliptical arcs facing each other, wherein at least one of said
third side and said fourth side is substantially straight, and a
distance between said third side and said fourth side is smaller
than a distance between said two elliptical arcs.
2. The inspection apparatus according to claim 1, further
comprising: a casing which stores said lenses; and two elliptical
arcs facing each other, wherein: a shape of a cross-section of said
casing is elliptical, the shape of the cross-section includes a
fifth side and a sixth side facing each other, at least one of said
fifth side and said sixth side being substantially straight, and a
distance between said fifth side and said sixth side is smaller
than a distance between said arcs.
3. The inspection apparatus according to claim 1, wherein said
first side and said second side form straight lines which face each
other, and said two straight lines are substantially parallel with
each other.
4. The inspection apparatus according to claim 3, wherein said
objective lens is set substantially parallel to said lenses.
5. The inspection apparatus according to claim 1, further
comprising a spatial filter arranged between said aberration
correcting system and said sensor.
6. The inspection apparatus according to claim 1, wherein said
lenses are set substantially parallel to each other.
7. The inspection apparatus according to claim 1, wherein said
irradiation system forms an irradiation area, wherein said
irradiation area is substantially a line.
8. The inspection apparatus according to claim 7, wherein a
projection line of a detection axis of said detection system
crosses said line.
9. The inspection apparatus according to claim 7, wherein a
projection line of a detection axis of said detection system is
substantially parallel to said line.
10. The inspection apparatus according to claim 1, further
comprising a second detection system which is arranged in different
position from said detection system, wherein said second detection
system includes second aberration correction system, wherein said
second aberration correction system comprises a plurality of second
lenses lining up in a direction including an axis of said second
lenses, wherein said second lenses have substantially elliptical
shapes, each of said elliptical shapes including a 7th side and 8th
side facing each other, and two elliptical arcs facing each other,
wherein at least one of said 7th side and 8th side is substantially
straight, and a distance between said 7th side and 8th side is
smaller than a distance between said two elliptical arcs, wherein
said second detection system includes a second sensor for detecting
light corrected by said second aberration correction system, and
wherein said second detection system includes a second objective
lens, said second objective lens being arranged between a mounting
position of said object and said second aberration correction
system, wherein said second objective lens has substantially
elliptical shapes, each of said elliptical shapes including a 9th
side and 10th side facing each other, and two elliptical arcs
facing each other, wherein at least one of said 9th side and said
10th side is substantially straight, and a distance between said
9th side and said 10th side is smaller than distance between said
two elliptical arcs.
11. The inspection apparatus according to claim 10, wherein at
least two of said first side, said second side, said 9th side, and
said 10th side are parallel.
12. The inspection apparatus according to claim 1, wherein said
irradiation system and said detection system comprises a dark field
imaging system.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a defect inspection system for
detecting a foreign material and a defect produced in a process for
manufacturing a large scale integration (LSI) semiconductor device
or a flat display substrate.
2. Description of the Related Art
In the process for manufacturing a semiconductor LSI, for example,
a foreign material or a defect pattern present on a substrate
(wafer) may cause a malfunction such as a short circuit and
insulation. With the tendency of reducing the size of a
semiconductor element, a micro foreign material and a defect
pattern cannot be ignored as the cause of the malfunction.
Therefore, the importance of the following technique is increased:
a technique for inspecting a foreign material and a defect during
the process for manufacturing a semiconductor wafer and for
managing the yield in order to take measures for reducing
defects.
Defect inspection techniques are mainly divided into two methods, a
bright field imaging method and a dark field imaging method. The
bright field imaging method is to illuminate a sample and detect
light (zero-order diffracted light) specularly reflected from the
sample, while the dark field imaging method is to detect scattered
light, without detecting the light (zero-order diffracted light)
specularly reflected from the sample.
Each of JP-A-2005-283190 and Japanese Patent No. 3566589 discloses
a technique using the dark field imaging method. JP-A-2005-283190
describes a technique for using a plurality of illumination
sections and switching between light paths of the illumination
sections based on the type of a foreign material or a defect.
Japanese Patent No. 3566589 describes a technique for illuminating
a sample substrate having a circuit pattern formed thereon with
beams substantially parallel to each other in a longitudinal
direction of an elongated beam spot formed by the beams, the beams
propagating in a direction corresponding to a predetermined angle
with respect to a normal to the substrate, a predetermined angle
with respect to main straight lines of the circuit pattern and a
substantial right angle with respect to the direction of scanning
the sample substrate mounted on a stage.
SUMMARY OF THE INVENTION
The defect inspection technique using the dark field imaging method
is to improve inspection sensitivity by receiving a large amount of
signals output from a defect to be scanned and to suppress signals
output from other parts such as a regular circuit pattern on the
surface of a substrate.
The principle of a dark field imaging method related to the present
invention will be clarified. First, a sample is opaque to an
illumination light beam. The illumination light beam incident on
the sample is specularly reflected, diffracted, or scattered (above
the sample (in an upper hemisphere)) on the surface of the sample,
or a foreign material or a defect. It is preferable that light
derived from the foreign material or the defect be detected and
that light derived from other parts such as a regular circuit
pattern on the surface of the substrate be not detected. To achieve
this preferable configuration, the incident direction (defined by
an elevation angle formed between the direction of traveling of the
illumination light beam and the surface of a sample and an azimuth
angle formed between the direction of traveling of the illumination
light beam and a specified direction) of the illumination light
beam is specified, and the receiving direction (defined by an
elevation angle formed between the direction of traveling of light
scattered from the sample and the surface of sample and an azimuth
angle formed between the direction of traveling of the light
scattered from the sample and the specified direction) of light to
be received by a detection system is determined. The incident
direction of the illumination light beam and the receiving
direction of light to be received by the detection system in the
upper hemisphere characterize defect inspection techniques provided
in respective optics systems.
An actual defect inspection system encounters problems in the
abovementioned principle and in the mechanical configuration of an
optics system. In other words, it is necessary that a limitation of
an installation space be considered.
Regarding conventional techniques, an optical lens (objective lens)
for receiving light, which is shown in FIGS. 12 and 13 of Japanese
Patent No. 3566589, has a circular shape. The circular lens is
provided in a casing (refer to FIG. 1 of JP-A-2005-283190). This
causes a limitation of an installation space, causing difficulty in
improvement of inspection sensitivity.
To avoid the above problem, a technique for covering the entire
surface of the upper hemisphere with a small-diameter fiber can be
considered. This technique, however, causes the configuration of
the system to be complicated, and has not been put into practical
use yet.
It is, therefore an object of the present invention to provide a
defect inspection system capable of detecting a defect and the like
present on the surface of a sample with high sensitivity by
suppressing an effect of light scattered from a rough surface of
the sample and a regular circuit pattern and increasing a gain of
the light scattered from a defect or a foreign material.
According to the present invention, an optical lens is arranged
between a sample to be inspected and detection unit for detecting
light scattered from the surface of a sample which is irradiated
with an illumination light beam. The optical lens focuses the
scattered light on the detection unit. The length in the azimuth
direction is made larger than the length in the elevation direction
with respect to the surface of the sample to be inspected
The defect inspection system according to the present invention is
capable of suppressing an effect of light scattered from a rough
surface of the sample to be inspected and a regular circuit pattern
and increasing a gain of the light scattered from a defect and a
foreign material to detect a defect and the like present on the
surface of a sample with high sensitivity.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a top view of an optics system for detection, explaining
the principle of the present invention.
FIG. 1B is a diagram showing the configuration of the optics system
for detection, explaining the principle of the present
invention.
FIGS. 2A and 2B are each a diagram showing the positional
relationship between the optics system for detection and an optics
system for illumination, explaining the principle of the present
invention.
FIGS. 3A to 3C are each a diagram showing characteristics of
distribution of light reflected on and scattered from a defect and
a back surface of a thin film, explaining the principle of the
present invention.
FIGS. 4A to 4E are each a diagram showing the relationship between
an aperture of the lens for detection and an elevation angle of an
optical lens for detecting in oblique direction.
FIGS. 5A and 5B are each a diagram showing a semiconductor wafer
with LSI arranged thereon, which is an inspection sample of the
present invention.
FIG. 6 is a diagram explaining an effect of the present
invention.
FIGS. 7A and 7B are each a diagram explaining a difference in
effect between an adjusted elliptical lens according to the present
invention and a circular lens.
FIG. 8 is a diagram showing an example of an arrangement in which a
plurality of the adjusted elliptical lenses are provided at
positions corresponding to elevation angles different from each
other, explaining the effect of present invention.
FIG. 9 is a diagram explaining the effect of the present
invention.
FIGS. 10A to 10C are each a diagram showing a modification of an
embodiment of the present invention.
FIGS. 11A to 11C are each a diagram explaining a difference in
defect accumulation between illumination at a low elevation angle
with respect to the surface of the sample and illumination at a
high elevation angle with respect to the surface of the sample.
FIG. 12 is a diagram showing an example of a modification of the
present invention.
FIG. 13 is a diagram showing another example of the modification of
the present invention.
FIG. 14 is a diagram showing the configuration of a defect
inspection system applied to the present invention.
FIG. 15 is a diagram showing three beam spot imaging sections of
the optics system for illumination.
FIGS. 16A and 16B are each a diagram explaining a method for
forming an elongated beam spot.
FIG. 17 is a diagram explaining the method for forming the
elongated beam spot.
FIG. 18 is a diagram showing an example of the arrangement of three
beam spot imaging sections provided in the optics system for
illumination.
FIG. 19 is a diagram showing an optics system for detection of
light scattered upwardly with respect to the surface of the
sample.
FIG. 20 is a diagram showing an example of a modification of the
optics system for detection of light scattered at a right angle and
almost right angle, as shown in FIG. 19.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will be described with
reference to the accompanying drawings.
First, the principle of the present invention will be described.
FIG. 1A is a top view of an optics system (hereinafter referred to
as a "detection optics system") for detection of light. FIG. 1B is
a diagram showing the configuration of a system for efficiently
detecting a distribution of light scattered from a defect present
on a silicon wafer. In FIGS. 1A and 1B, a wafer to be inspected is
placed on a sample scanning mechanism 600, and is illuminated by an
optics system for illumination with an illumination beam 2 from an
oblique direction with respect to the surface of the silicon wafer.
The optics system has an optical source 1. The illumination beam 2
is distributed on the silicon wafer to form, on the silicon wafer,
a beam spot having an elongated shape with a longer axis
perpendicular to a direction of scanning of a stage. If a defect is
present on the silicon wafer, the light 4 scattered from the defect
is received by an optics system (a lens 10) for detection. The
detection optics system is arranged at a position to ensure that an
imaginary line extending between the center of the lens 10 and the
center of a beam spot is inclined with respect to the surface of
the silicon wafer. An optical image obtained by the detection
optics system is converted into an electrical signal by a
photoelectric converter 5. A part of the electrical signal is
transmitted through a signal receiver 604 directly to a signal
processor 606, and processed by the signal processor 606. The
remaining part of the electrical signal is transmitted through a
reference signal memory 605 to the signal processor 606. The signal
processor 606 is designed to detect a defect, determine whether the
defect is true or false, classify the type of the defect, and
determine the shape of the defect.
A system controller 602 controls a series of the signal processing,
operations for the above-mentioned determinations, a command to a
mechanism controller 601, and transmission and reception of a
signal from and to a user interface 603.
Next, FIGS. 2A and 2B are each a diagram explaining the positional
relationship between an optics system for illumination and the
detection optics system. In FIG. 2A, an optical source 1 drawn on
the left bottom side of FIG. 2A emits an illumination light beam 2.
In this case, the illumination light beam is specularly reflected
on the wafer to form light 3, which travels in a direction on the
right top side of FIG. 2A. The optics system (hereinafter referred
to as the "oblique detection optics system") for detection of light
scattered at an acute angle with respect to the surface of the
sample can be installed in any azimuth direction with respect to
the center of the beam spot formed on the wafer (in a horizontal
direction with respect to the surface of the wafer) to ensure that
the specularly reflected light 3 is not received by the oblique
detection optics system. FIG. 2B is a side view of the arrangement
with the optics system for illumination and the detection optics
system. The following two angles can be adjusted: the incident
angle (elevation angle) of scattered light 4 emitted by the optics
system for illumination with respect to the surface of the wafer;
and the output angle (elevation angle) of the scattered light 4
with respect to the surface of the wafer. To detect a defect with
high sensitivity, the value of the elevation angle is set to be low
since a signal with a high signal-to-noise ratio is detected from
the defect.
FIGS. 3A to 3C are diagrams each showing a distribution of light
scattered from a rough surface of a wafer. In FIG. 3A, the surface
of a wafer 7 is illuminated with the illumination light beam 2 from
an oblique direction, and light 20a scattered from a defect 20 is
intensively distributed into a space, which is similar to a space
of the distribution of the illumination light beam 2 specularly
reflected. As shown in FIG. 3B, light 21a is scattered from a rough
surface 21 (regular portion) of the wafer 7, such as grains, and is
relatively widely distributed. The amount of components of the
light 21a directing to a detector 5 is small.
Thus, the detector 5 is installed to ensure that the optics system
detects the light scattered at a low elevation angle with respect
to the surface of the wafer 7, resulting in the fact that the
amount of the light scattered from the rough surface of the wafer 7
is small and the oblique detection optics system effectively
receives a signal from the defect. As shown in FIG. 3C, if the
surface of the wafer 7 is covered with a transparent oxide film,
the amount of light 22c reflected from the defect 22 at a low
elevation angle with respect to the surface of the wafer 7 is
smaller than that of light 22a reflected from the defect 22 at a
high elevation angle with respect to the surface of the wafer 7 at
an interface 7a of the oxide film due to reflectivity of the
surface of the oxide film and distribution of transmissivity (since
light 22b reflected from the defect 22 is separated from the light
22c). In this case, it is necessary that the detector 5 be
installed in the vicinity of the wafer 7 to receive light reflected
from the defect 22 at a low elevation angle with respect to the
surface of the wafer 7 since the detector 5 detects a signal coming
from the defect 22 on a bottom surface of the oxide film with high
sensitivity and with low susceptibility to light scattered from the
rough bottom surface of the transparent oxide film 7a or a circuit
pattern.
FIGS. 4A to 4e each show the configuration of the detection optics
system in the case of detection of light scattered at an acute
angle with respect to the surface of the wafer 7. If the detection
optics system detects light with high sensitivity, an angle of an
aperture for receiving light from a lens needs to be large. FIG. 4A
shows an optics system with a lens having a large numerical
aperture (NA). In FIG. 4, the outer diameter of the lens is a value
of 10a, and an angle formed between the surface of the wafer 7 and
a direction of traveling of the light 4 is a value of .alpha.1.
FIG. 4B shows the case where the oblique detection optics system
receives the light 4 reflected from the defect at a reduced
elevation angle .alpha.2 with respect to the surface of the wafer 7
to reduce light scattered from a rough surface of the wafer 7, a
rough bottom surface of the oxide film, and a circuit pattern, and
to increase the amount of the light, which is scattered from the
defect and is to be detected. In this case, the elevation angle
.alpha.2 can be set to be smaller than the elevation angle
.alpha.1. The outer diameter 10b of the lens, however, is smaller
than the outer diameter 10a of the lens. As a result, the lens
having the outer diameter 10b has a lower ability to focus the
scattered light than that of the lens having the outer diameter
10a.
If the lens shown in FIG. 4C has an outer diameter 10c similar to
the outer diameter 10a shown in FIG. 4A to increase the ability to
focus the scattered light, the lens interferes with the wafer
7.
To avoid the interference, a portion of the lens, which
interferences with the wafer 7, is removed. The lens with the
portion removed is shown in FIGS. 4D and 4E. The removal of the
portion which interferences with the wafer 7 allows the lens to
have an aperture larger than that of the lens having the outer
diameter 10b while the elevation angle .alpha.2 is maintained. This
makes it possible to improve the ability to detect the scattered
light and performance of the lens simultaneously. In FIG. 4E, a
portion of the lens shown in FIG. 4D, which is located on the
opposite side of the removed portion, is removed to form an
adjusted elliptical lens. The adjusted elliptical lens shown in
FIG. 4E can reduce its volume in an elevation direction parallel to
a normal to the direction of traveling of the light 4 reflected
from the sample at the elevation angle .alpha.2. The adjusted
elliptical lens allows the oblique detection optics system with
high lens performance to be installed. The optics system is also
assembled with high density implementation in an elevation
direction. A plurality of the oblique detection optics systems
makes it possible to increase information to be detected from a
defect, resulting in the fact that the ability to detect the defect
and the ability to classify the type of the defect can be
improved.
Next, a description will be made of the definition of the shape of
the adjusted elliptical lens. The adjusted elliptical lens has a
shape obtained by cutting a circular lens by use of two cutting
lines parallel to each other. The adjusted elliptical lens has two
straight sides parallel to each other and two elliptical arcs
located symmetrically to a central axis thereof, which is
perpendicular to the two straight sides. The distance between the
two straight sides is smaller than the maximum length of an
imaginary line extending between the two elliptical arcs, the
imaginary line being parallel to the two straight sides.
As examples of values of the optics system, the NA in an elevation
direction (parallel to a normal to the direction of traveling of
the light, which is scattered from the sample and is to be detected
by the optics system) can be 0.12, the NA in an azimuth direction
(parallel to the surface of the sample) can be 0.45, and the
elevation angle can be 12 degrees.
Next, with reference to FIGS. 5A and 5B, a description will be made
of a sample to be inspected by a defect inspection system according
to the present invention. A semiconductor wafer 1a shown in FIG. 5A
has chips 1aa two-dimensionally arranged at a predetermined
interval. Each of the chips 1aa is composed of a memory LSI. Each
of the chips 1aa mainly includes: a memory cell area 1ab; a
peripheral circuit area 1ac composed of a decoder, a control
circuit and the like; and another area 1ad. The memory cell area
1ab has a repetitive memory cell pattern with memory cells
regularly arranged in a two-dimensional manner. The peripheral
circuit area 1ac has a non-repetitive pattern with circuits
irregularly arranged in a two-dimensional manner.
A semiconductor wafer 1b shown in FIG. 5B has chips 1ba, each of
which is composed of LSIs such as microcomputers two-dimensionally
arranged at a predetermined interval. Each of the chips 1ba mainly
includes: a register area 1bb, a memory area 1bc, a central
processing unit (CPU) core area 1bd, and an input/output area 1be.
FIG. 5B is a conceptual diagram showing the arrangement including
the memory area 1bc, the CPU core area 1bd and the input/output
area 1be. The register area 1bb has a repetitive pattern with
registers regularly arranged in a two-dimensional manner, and the
memory area 1bc has a repetitive pattern with memories regularly
arranged in a two-dimensional manner. The CPU core area 1bd has a
non-repetitive pattern with CPU cores irregularly arranged, and the
input/output area 1be has a non-repetitive pattern with
input/output sections irregularly arranged. As described above, the
samples 1 to be inspected by the defect inspection system according
to the present invention, which are the semiconductor wafers 1a and
1b shown in FIGS. 5A and 5B respectively, have chips regularly
arranged. In each of the chips, the minimum line width varies
depending on the area. Also, some of the areas each have a
repetitive pattern and the remaining areas each have a
non-repetitive pattern. Various configurations can be considered
depending on the areas.
Next, a description will be made of effects of the oblique
detection optics system using the adjusted elliptical lens shown in
FIG. 4D and the oblique detection optics system using the adjusted
elliptical lens shown in FIG. 4E when the sample shown in FIG. 5A
or the sample shown in FIG. 5B is used.
Effect 1
It is possible to install the oblique detection optics system with
a high numerical aperture (aperture ratio) at a position
corresponding to a low elevation angle formed between the direction
of traveling of light scattered from the sample and the surface of
the sample. As shown in FIG. 6, the oblique detection optics system
is configured to ensure that the sample is illuminated with light
through illumination lenses 110, 120 and 130 and that a detector
501 detects light scattered from the sample through an adjusted
elliptical lens 502. In the oblique detection optics system, an
aperture angle of the adjusted elliptical lens can be large in the
horizontal direction (parallel to the surface of the sample) to
improve the optical performance.
With reference to FIGS. 7A and 7B, a circular lens 10A mounted in a
casing 30 and an elliptical lens 10B mounted in a casing 31 are
compared with each other. If an elevation angle is .alpha.2 in
FIGS. 7A and 7B, the aperture angle of the elliptical lens 10B can
be larger than that of the circular lens 10A in the horizontal
direction.
Effect 2
It is possible to detect a high signal-to-noise ratio since the
numerical aperture is determined based on the difference between
characteristics of the scattered light.
Returning back to FIGS. 3A to 3C, it is understood that, in the
case where the sample is illuminated with the light beam from the
oblique direction, and light scattered from the sample is detected
in a direction other than the direction of traveling of the
specularly reflected light, the ability to detect the light can be
improved by reducing the aperture angle in the elevation direction
to reduce background noise caused by irregular grains and
increasing the aperture angle in the azimuth direction to increase
the amount of the light scattered from the defect. It is,
therefore, understood that the adjusted elliptical lens is optimal
to detect the scattered light with high sensitivity.
The above description was made of the oblique detection optics
system in which the light reflected at a low elevation angle with
respect to the surface of the sample is detected. However, it has
been reported that it is effective to detect a defect present on a
part of a pattern by using the optics system for irradiating the
illumination light beam at a high elevation angle with respect to
the surface of the sample, and the optics system (hereinafter
referred to as the "upward detection optics system) for detection
of light scattered upwardly with respect to the surface of the
sample. In this case, it is possible to improve the ability to
detect the scattered light by using the adjusted elliptical lens of
the upward detection optics system and by adjusting aperture angles
in two directions perpendicular to each other.
In order to obtain the abovementioned effects, the adjusted
elliptical lens can be provided only in the upward detection optics
system.
Effect 3
It is possible to achieve a detection optics system, which is
assembled with high density implementation by using a flat optical
lens for detection.
The adjusted elliptical lens with a small aperture angle in the
elevation direction and a large aperture angle in the azimuth
direction can be installed in a small space in the elevation
direction. As shown in FIG. 8, a plurality of the adjusted
elliptical lenses 502 can be provided with high density
implementation in the elevation direction and with a small gap
between the adjusted elliptical lenses. The detection optics system
can be arranged with high density implementation in the elevation
direction and at an optimal elevation angle appropriate for
characteristics of light scattered from the defect. The detection
optics system is capable of detecting the defect with high
efficiency. In addition, this arrangement makes it possible for the
optics system to detect a small or minute defect with detection
ability improved. Furthermore, the arrangement makes it possible to
install a plurality of the detectors to categorize defects. The
method for categorizing defects will be described in Effect 4.
Effect 4
It is possible to discriminate scattering characteristics and
categorize defects by using the plurality of detectors.
The light scattered from the defect varies in elevation angle, at
which the scattered light is reflected, depending on the type of
the defect. The types of the defects include an attached foreign
material, a scratch, a short circuit occurring in a circuit
pattern, a disconnection occurring in a circuit pattern, and a pit.
Although it is necessary to detect and categorize such defects, the
directions of light scattered from such defects may be different
depending on the type of the defect. For example, as shown in FIGS.
10A to 10C, three or more of the adjusted elliptical lenses 502 are
installed at positions defined by the same azimuth directions and
elevation directions different from each other, or at positions
defined by the same elevation direction and azimuth directions
different from each other, or at positions defined by azimuth
directions different from each other and elevation directions
different from each other to achieve an oblique detection optics
system 503 with high density implementation. The oblique detection
optics system 503 is adapted to detect light scattered from a
defect present on the sample at an acute angle with the surface of
the sample. The plurality of detectors 501 are capable of detecting
light scattered from the defect. This makes it possible to
determine a direction of traveling of the light scattered at a low
elevation angle and at a high elevation angle and to categorize the
defect based on the direction of the scattered light. In addition,
the direction of the scattered light to be detected varies
depending on the direction of the illumination light beam,
resulting in the fact that information on the categories can be
increased.
FIGS. 11A to 11C are diagrams to compare a case example in which a
sample is detected by using light incident on the sample at a high
elevation angle with respect to the surface of the sample, with a
case example in which a sample is detected by using light incident
on the sample at a low elevation angle with respect to the surface
of the sample. As shown in FIGS. 11A to 11C, it is understood that
the types of the defects can be discriminated based on the
elevation angle of the illumination light beam with respect to the
surface of the sample, an azimuth angle of the detected light with
respect to a specified direction, and the elevation angle of the
detected light with respect to the surface of the sample. A
polarization state of the light to illuminate the defect is
selected from among S-polarized light, P-polarized light,
circularly-polarized light, and non-polarized light to ensure that
a condition for spatial distribution of the scattered light is
varied. By using the polarization condition, the ability to
estimate the type of the detected defect can be improved. The
plurality of detectors provide a great effect to improve the
ability to categorize the defect.
Effect 5
An anisotropic aperture of the detection optics system is
advantageous based on conditions for illumination performed by the
optics system for illumination to form a beam.
Here, a beam to be formed by the detection optics system is
compared with the beam to be formed by the optics system for
illumination. As shown in FIG. 9, in the detection optics system,
an elongated beam spot of the illumination light beam is formed
without the illumination light beam being focused, the length of
the illumination light beam being perpendicular to the direction of
scanning of the stage. The illumination light beam is focused to
concentrate on illumination power in the direction (the elevation
direction) perpendicular to the direction of scanning of the stage.
That is, the illumination light beam is incident on the surface of
the wafer at an elevation angle with respect to the surface of the
wafer in order to inspect the wafer. In the case where the light is
reflected on the wafer to be inspected, an aperture angle in the
azimuth direction (horizontal direction is required to be large for
the lens of the detection optics system as a condition necessary
for detecting a defect (since the illumination light is parallel
light). However, it is not necessary that an aperture angle in the
elevation direction be large for the lens of the detection optics
system. In the case of using the adjusted elliptical lens, the
condition for the aperture matches with the condition for the beam
formation performed by the optics system for illumination, and it
is necessary that the aperture of the detection optics system be
based on the numerical aperture (NA) of the optics system for beam
formation, which is provided in the optics system for illumination,
resulting in the fact that the optics system can detect a defect
with high efficiency.
It should be noted that use of some of the aperture angles of the
detection optics system makes it possible to efficiently detect a
defect. The detection optics system is installed to obtain aperture
angles in two directions perpendicular to each other and is capable
of detecting a defect with high efficiency even if a part of the
detection optics system having a circular lens with an isotropic
aperture is used to change the aperture angle. As shown in FIG. 12,
when the scattered light is blocked by an upper half portion of an
isotropic optical lens 5020 for detection and a lower half portion
of the isotropic optical lens 5020 is used as an aperture thereof,
the aperture angle in the two directions perpendicular to each
other can be changed, resulting in improvement of an effect to
change an intensity ratio of a signal coming from a defect to a
background signal. This can achieve an increase in sensitivity for
detection of the defect.
In addition, the upward detection optics system and the oblique
detection optics system can be installed at positions different
from each other to achieve the best detection performance,
respectively.
When the upward detection optics system and the oblique detection
optics system are used to improve the sensitivity for detection of
the defect, the two optics systems preferably measure the same
location simultaneously to reduce a throughput time. In this case,
the conditions for irradiation of the illumination light beam, such
as an elevation angle, an azimuth angle, and polarization
conditions, are limited to a single type of the conditions. There
are many cases where the optimal conditions for illumination vary
depending on the defect to be detected and on the combination of
the upward detection optics system and the oblique detection optics
system. It is necessary to change illumination conditions for each
of the two optics systems in order to detect a defect with high
sensitivity under the optimal conditions for irradiation of the
illumination light beam by using the upward detection optics system
and the oblique detection optics system. As shown in FIG. 13, each
of the upward detection optics system and the oblique detection
optics system simultaneously performs a single inspection under the
illumination conditions for each of the upward detection optics
system and the oblique detection optics system, the illumination
conditions for the upward detection optics system being different
from the illumination conditions for the oblique detection optics
system. The simultaneous inspections performed by the two detection
optics systems make it possible to detect a defect with high
sensitivity. In this case, the two detection optics systems are
installed at positions different from each other.
FIG. 14 is a diagram showing the configuration of the defect
inspection system applicable to the present invention. The defect
inspection system shown in FIG. 14 includes a stage section 300, an
optics system 100 for illumination, an optics system (hereinafter
referred to as a "upward detection optics system") 200 for
detection of light scattered upwardly with respect to the surface
of a sample, an optics system (hereinafter referred to as a
"oblique detection optics system") 500 for detection of light
scattered obliquely with respect to the surface of the sample, and
a control system 400. The stage section 300 is adapted to move a
sample such as a wafer in an X-axis direction, Y-axis direction,
and Z-axis direction and to rotate around the Z-axis. The optics
system 100 is adapted to irradiate illumination light beam on the
sample for detection of a defect. The upward detection optics
system 200 is adapted to detect light reflected from the sample.
The oblique detection optics system 500 is adapted to detect light
reflected from the sample. The control system 400 is adapted to
execute arithmetic processing, signal processing, and the like.
The stage section 300 has an X stage 301, a Y stage 302, a Z stage
303, a rotation stage 304, and a stage controller 305. The optics
system 100 for illumination has a laser source 101, a beam expander
composed of a concave lens 102 and a convex lens 103, a beam
formation section composed of an optical filer group 104 and a
mirror 105, and first, second and third beam spot imaging sections
110, 120 and 130. The first beam spot imaging section 110 includes
an optical branching element (or a mirror) 106, an illumination
lens 107 having a conic surface, and mirrors 108 and 109. The
optical filter group 104 includes a neutral density (ND) filter and
a wavelength plate.
As the laser source 101, a third-harmonic generation (THG) of a
high power YAG laser is preferably used. The THG has a wavelength
of 355 nm. It is not necessary that the THG necessarily have the
wavelength of 355 nm. In addition, it is not necessary that the YAG
laser and the THG are necessarily used as the laser source 101.
Specifically, as the laser source 101, an Ar laser, a nitrogen
laser, an He--Cd laser, an excimer laser, or the like may be
used.
The upward detection optics system 200 has a detection lens 201, a
space filter 202, an imaging lens 203, a zoom lens group 204, a
one-dimensional detector (image sensor) 205, a space filter
controller 207, and a zoom lens controller 208. The oblique
detection optics system 500 has a one-dimensional detector (image
sensor) 501, an objective lens 502, a space filter 503, and an
imaging lens 504. The one-dimensional detector 205 may be a time
delay integration (TDI) sensor. The control system 400 has an
arithmetic processor 401, a signal processor 402, an output section
403, and an input section 404. The arithmetic processor 401 has a
central processing unit (CPU) and the like and controls a driving
system such as a motor, coordinates, and the sensors. The signal
processor 402 has: an analog-digital converter, a data memory
capable of delaying data, a differential processing circuit for
calculating a difference between signals supplied from chips, a
memory for temporarily storing a signal indicative of the
difference between the signals supplied from the chips, a threshold
calculator for setting a pattern threshold, comparator, and the
like.
The output section 403 is adapted to store a result of detection of
a defect such as a foreign material and to output or display the
result of detection of the defect. The input section 404 is adapted
to input a command and data to the arithmetic processor 401 in
accordance with an operation performed by a user. A system of
coordinates is shown at the lower left of FIG. 14. In FIG. 14, an X
axis and a Y axis are plotted in a horizontal plane, and a Z axis
is plotted in a vertical direction. The horizontal plane is
parallel to the surface of the sample, and the vertical direction
is perpendicular to the surface of the sample. The upward detection
optics system 200 has an optical axis parallel to the Z axis, and
the oblique detection optics system 500 has an optical axis
parallel to the horizontal plane xz.
The three beam spot imaging sections 110, 120 and 130 of the optics
system 100 for illumination will be described with reference to
FIGS. 15 and 16. FIG. 15 is a top view of a sample 1 which is a
wafer. In FIG. 15, an illumination light beam 11 is irradiated on
the surface of the sample 1 from the X-axis direction through the
first beam spot imaging section 110. An illumination light beam 12
is irradiated on the surface of the sample 1 from a direction
inclined at an angle of 45 degrees with respect to the Y-axis
direction in the horizontal plane through the second beam spot
imaging section 120, and an illumination light beam 13 is
irradiated from a direction inclined at an angle of 45 degrees with
respect to the Y-axis direction and perpendicular to the direction
of traveling of the illumination light beam 12 in the horizontal
plane through the third beam spot imaging section 130. The oblique
detection optics system 500 is installed at a position on the
opposite side of the first beam spot imaging section 110 with
respect to the sample 1.
The illumination light beams 11, 12 and 13 are irradiated on the
surface of the sample 1 at a predetermined elevation angle .alpha.
with respect to the surface of the sample 1. In particular, the
elevation angle .alpha. of the illumination light beams 12 and 13
can be reduced to decrease the amount of light to be detected
scattered from the bottom surface of a thin transparent film. The
illumination light beams 11, 12 and 13 form an elongated beam spot
3 on the sample 1. The length of the beam spot 3 is extended in the
Y-axis direction, and is larger than a diameter of a light
receiving area 4 of the one-dimensional detector 205 provided in
the upward detection optics system 200. A description will be made
of the reason for installations of the three beam spot imaging
sections 110, 120 and 130 in the optics system 100 for
illumination. When an angle formed between the direction of
traveling of the illumination light beam 11 and the direction of
traveling of the illumination light beam 12 in the horizontal plane
is .beta.1, and an angle formed between the direction of traveling
of the illumination light beam 13 and the X-axis direction is
.beta.2, .beta.1=.beta.2=45 degrees in the embodiment of the
present invention. This arrangement makes it possible to prevent
light diffracted in zero order from a non-repetitive pattern on a
substrate of the sample 1 from being incident on the objective lens
201 of the upward detection optics system 200.
The non-repetitive pattern on the substrate of the sample 1 is
mainly composed of linear patterns each having lines, which are
parallel or perpendicular to the lines of another one of the linear
patterns. The lines of each of the linear patterns are parallel to
the X-axis direction or the Y-axis direction. The pattern formed on
the substrate of the sample 1 projects, and a recessed portion is
formed between the adjacent linear patterns. The illumination light
beams 12 and 13 emitted from directions inclined at an angle of 45
degrees with respect to the X and Y axes are blocked by the circuit
pattern which projects, and cannot be irradiated on the recessed
portion formed between the linear patterns. The beam spot imaging
section 110 is provided on the X axis to emit the illumination
light beam 12 for detection of a defect. Thus, the illumination
light beam 11 can be irradiated on the recessed portion between the
adjacent linear patterns to detect a defect such as a foreign
material present on the recessed portion. The sample may be rotated
by 90 degrees based on the direction of the lines of the linear
pattern to ensure that the sample is inspected. Alternatively, the
illumination light beam 11 may be irradiated on the sample from the
Y-axis direction to inspect the sample. When the illumination light
beam is irradiated on the sample in the X-axis direction, i.e., on
the recessed portion formed between the adjacent linear patterns as
is the illumination light beam 11, it is necessary that the
detector block zero-order diffracted light to ensure not to detect
the zero-order diffracted light. To block the zero-order diffracted
light, the space filter 202 is provided.
Next, with reference to FIGS. 16A, 16B and 17, a method for forming
an elongated beam spot 3 will be described. Each of FIGS. 16A and
16B shows the laser source 101, the concave lens 102, the convex
lens 103 and the illumination lens 104, which are provided in the
optics system 100 for illumination. The other elements 105, 106,
107, 108, and 109 of the optics system 100 are omitted in FIGS. 16A
and 16B. The illumination lens 104 is cylindrical, that is, has a
conic shape. As shown in FIG. 16A, the focal length of the
illumination lens 104 is linearly varied in a longitudinal
direction thereof. As shown in FIG. 16B, the illumination lens 104
has a cross section of the shape of a flat convex lens.
As shown in FIG. 17, the illumination light beam is incident on the
sample 1 at an elevation angle .alpha.1 with respect to the surface
of the sample 1 with a reduction in the aperture of the
illumination lens in the Y-axis direction, the illumination light
beam being collimated in the X-axis direction. The illumination
light beam forms an elongated beam spot 3 on the surface of the
sample 1. In FIG. 17, an angle of the illumination light beam with
respect to the surface of the sample 1 is .alpha.1 and an image of
the illumination light beam irradiated on the sample 1 is formed in
a direction inclined at an angle of .beta.1 with respect to the
X-axis direction. The use of the illumination lens 104 makes it
possible to collimate the illumination light beam in the X-axis
direction and to form the image of the illumination light beam in
the direction inclined at the angle of .beta.1, which is
approximately 45 degrees, with respect to the X-axis direction.
Next, a description will be made of an example of the configuration
of the three beam spot imaging sections 110, 120 and 130 in the
optics system 100 for illumination with reference to FIG. 18. In
FIG. 18, the laser source 101 emits a laser beam, which is divided
into two light beams by a first optical element 141 for branching
of light such as half mirror. One of the light beams is reflected
by a mirror 142 and a mirror 143 and incident on a concave lens 144
constituting the first beam spot imaging section 110. In this way,
the illumination light beam 11 is generated by the first beam spot
imaging section 110.
The other one of the light beams is divided into two light
sub-beams by a second optical element 145 for branching of light
such as a half mirror, the light sub-beams directing to light paths
different from each other. One of the light sub-beams is reflected
by a mirror 146 and incident on a concave lens 147 constituting the
second beam spot imaging section 120. In this way, illumination
light beam 12 is generated by the second beam spot imaging section
120. The other one of the light sub-beams is incident on a concave
lens 148 constituting the third beam spot imaging section 130. In
this way, illumination light beam 13 is generated by the third beam
spot imaging section 130.
When the first optical element 141 is removed from the light path
or replaced with an optical element 141a, which passes light
without reflecting and branching the light, the illumination light
beam 11 is not generated by the first beam spot imaging section
110. That is, the illumination light beam 12 and the illumination
light beam 13 are only generated by the second beam spot imaging
section 120 and the third beam spot imaging section 130,
respectively. In addition, when the first optical element 141 is
removed from the light path or replaced with the optical element
141a, and the second optical element 145 is replaced with a mirror
145a for reflecting light without passing and branching the light,
the illumination light beam 13 is only generated by the third beam
spot imaging section 130.
When the first optical element 141 is removed from the light path
or replaced with the optical element 141a, and the second optical
element 145 is removed from the light path or replaced with an
optical element, which passes light without reflecting and
branching the light, the illumination light beam 12 is only
generated by the second beam spot imaging section 120. When the
first optical element 141 is installed and the second optical
element 145 is replaced with the mirror 145a, the illumination
light beam 11 and the illumination light beam 13 are only generated
by the first beam spot imaging section 110 and the third beam spot
imaging section 130, respectively.
When the first optical element 141 is installed, and the second
optical element 145 is removed or replaced with the optical
element, which passes light without branching and reflecting the
light, the illumination light beam 11 and the illumination light
beam 12 are only generated by the first beam spot imaging section
110 and the second beam spot imaging section 120, respectively. As
described above, the illumination light beams 11, 12 and 13 can be
selectively generated by the three beam spot imaging sections 110,
120 and 130.
Next, with reference to FIG. 19, a description will be made of the
upward detection optics system 200. In FIG. 19, the illumination
light beam is irradiated on the sample 1 to form an elongated beam
spot 3, and reflected by and scattered from the sample 1. The light
is output from upper and bottom surfaces of the transparent thin
film, a circuit pattern present on the substrate of the sample 1,
and a defect such as a foreign material. The output light is
received by the detector 205 via the detection lens 201, the space
filter 202 and the imaging lens 203 included in the upward
detection optics system 200, and photoelectrically converted by the
detector 205. Since the illumination intensity (power) of flux of
light emitted from the laser source 101 can be controlled by the ND
filter of the optical filter group 104 or by controlling laser
power, a dynamic range of output of the detector 205 can be
controlled.
Next, the space filter 202 will be described. The illumination
light beam is irradiated on the repetitive pattern present on the
sample 1 to form an interference fringe of diffracted light. When
the detector 205 receives the interference fringe of diffracted
light, an error signal is generated. In this case, the detector 205
cannot detect a defect such as a foreign material. The space filter
202 is arranged in a spatial frequency domain of the objective lens
201, i.e., at a location (corresponding to an exit pupil) of a
Fourier-transformed image in order to block the Fourier-transformed
image based on the light diffracted by the repetitive pattern.
As described above with reference to FIGS. 5A and 5B, the chip
formed on the wafer includes a repetitive pattern, a non-repetitive
pattern, and a part not having a pattern in general. The line width
of the repetitive pattern is varied depending on the circuit
pattern. It is general that as the space filter 202, a light
blocking pattern is set to block light frequently diffracted by the
repetitive pattern. As the space filter 202, the light blocking
pattern may be changed. Alternatively, as the space filter 202, a
plurality of light blocking patterns different from each other may
be provided. In any of the above cases, the light blocking pattern
may be changed or replaced based on the circuit pattern to block
the diffracted light.
As described above, when the illumination light beam 11 is
irradiated on the recessed portion between the linear patterns in
the X-axis direction, it is necessary that zero-order diffracted
light be blocked by the space filter 202. It is preferable that the
space filter 202 be installed to block not only the zero-order
diffracted light but also high-order diffracted light.
Next, a description will be made of a method for adjusting
detection sensitivity based on the size of a defect such as a
foreign material, which is to be detected. When the size of each of
pixels of the one-dimensional detector (image sensor) 205, such as
the TDI sensor, is reduced, the detector 205 can detect a smaller
defect such as a foreign material although the throughput of the
detector 205 is reduced, the size of each of the pixels being
measured based on an image formed on the sample 1 by the pixels of
the detector 205. In order to vary the size of the image formed on
the sample 1 by the pixels of the one-dimensional detector (image
sensor) 205, three types of the upward detection optics systems 200
are prepared.
To detect a defect such as a foreign material, having a length or a
diameter of 0.1 .mu.m or less, the upward detection optics system
200 having a small pixel size measured based on an image formed on
the sample 1 by the pixels thereof is selected for use. Lenses of
the zoom lens group 204 may be selected to ensure that the
configuration of the upward detection optics system 200 having the
small pixel size is achieved. For example, the configuration of the
lenses of the zoom lens group 204 may be designed to ensure that
the length of a light path from the sample 1 to the one-dimensional
detector 205 such as the TDI sensor is not varied. If it is
difficult to achieve the configuration of the zoom lens group 204,
a mechanism for controlling the distance between the sample 1 and
the one-dimensional detector 205 (image sensor) may be used in
addition to the selection of the lenses of the zoom lens group 204.
In addition, the one-dimensional detector 205 having a different
pixel size may be used.
Next, a description will be made of the oblique detection optics
system 500 with reference to FIG. 19. The optical axis of the
oblique detection optics system 500 is inclined at a predetermined
angle .beta. with respect to the surface of the sample 1. To reduce
the amount of light which is scattered from the bottom surface of
the transparent thin film and detected, the optical axis of the
oblique detection optics system 500 needs to be set to ensure that
light output at angles from 80 to 90 degrees with respect to the
surface of the sample 1 is detected. The adjusted elliptical lens
502 according to the present invention can be used to ensure that
the oblique detection optics system 500 is installed at a position
corresponding to a low elevation angle with respect to the surface
of the sample 1. Light reflected from the elongated beam spot
formed on the sample 1 is detected by the one-dimensional detector
(image sensor) 501 via the objective lens 502, the space filter 503
and the imaging lens 504.
In the example shown in FIG. 19, the one-dimensional detector
(image sensor) 501 is used to detect an image of the elongated beam
spot. The space filter 503 is adapted to block an interference
fringe of light diffracted from the repetitive pattern present on
the sample in the same manner as the space filter 202.
The outline of a method for detecting a defect such as a foreign
material will be described. In step S101 shown in FIG. 19, the
control system receives a signal from the one-dimensional detector
(image sensor) 205 of the upward detection optics system 200 to
execute high-speed parallel image processing on the received
signal. In step S103, the control system acquires an image to be
inspected. In step S104, the control system acquires an image
adjacent to the image to be inspected after delay processing in
step S102. Next, in step S105, the control system executes image
alignment processing to align the image to be inspected and the
adjacent image. Then, in step S106, the control system compares the
image to be inspected with the adjacent image.
In step S107, the control system determines a defect based on the
result of the comparison. In step S201, the control system receives
a signal from the one-dimensional detector (image sensor) 501 of
the oblique detection optics system 500 to execute high-speed
parallel image processing on the received signal. Steps S202 to
S207 are the same as step S102 to S107. The control system combines
information on the defect based on the result of the determination
in step S107 with information on the defect based on the result of
the determination in step S207 to make a comprehensive
determination. Lastly, in step S108, the control system combines
the defect detected by the upward detection optics system 200 with
the defect detected by the oblique detection optics system 500 to
generate a defect map.
In the example shown in FIG. 19, the defect inspection system
performs the defect determination in step S107 and the defect
determination in step S207. The defect inspection system may
perform both defect determinations in a single step to generate a
defect map.
Specifically, as shown in FIG. 20, the control system may compare
the result of the comparison in step S106 with the result of the
comparison in step S206 to perform the comprehensive determination
in step S107, and then generate a defect map in step S108.
Next, a description will be made of the case where the defect
inspection system according to the present invention inspects a
defect under a plurality of conditions. The inspection is performed
for the purpose of increasing the dynamic range, for example. Three
conditions are set based on power (high power, medium power, and
low power) of the illumination light. The three conditions
correspond to a priority on an area, a standard, and a priority on
sensitivity.
Under the three conditions, the defect inspection system inspects
the surface of the wafer, which is the sample, and combines results
of the inspections to generate an inspection result map (which is a
drawing in which a mark indicative of a defect such as a foreign
material detected from the sample 1 is plotted on position
coordinates). The inspection result map may be replaced with a
coordinates list of defects, or a list or map expressing levels of
detection signals obtained from defects. The defect inspection
system performs the inspection for the purpose of detecting a more
microscopic scratch or defect such as a foreign material, in
addition to the purpose of increasing the dynamic range. In this
case, conditions for the inspection includes scanning time of each
of the stages 301 and 302, angles .alpha.1, .beta.1 (including a
value of zero) and .beta.2 (including a value of zero) of the
illumination light beam generated by the optics system 100, and the
presence of the wavelength plate 104, and the like.
Next, a description will be made of a production line and a
production method for manufacturing a semiconductor and the like by
using the defect inspection system according to the present
invention. The semiconductor production line using the defect
inspection system according to the present invention includes a
manufacturing process, a probe inspection process, an inspection
system and a data analysis system. The manufacturing process,
especially, a process affecting the yield is always monitored by
the inspection system including the defect inspection system
according to the present invention. When any abnormality in the
processes is detected by the monitoring performed by the inspection
system, the process or the system, which causes the abnormality, is
identified by the inspection system.
In order to inspect a foreign material or a defect such as a
foreign material attached to a top surface of the sample in a
desired process with high accuracy of identification, it is
preferable that the defect inspection system according to the
present invention perform the inspection of a defect such as a
foreign material before and after the desired process to calculate
a logical difference between a result of the defect inspection
after the desired process and a result of the defect inspection
before the desired process.
It is not always that only a defect such as a foreign material
occurring in the desired process can be detected based on the
logical difference. The reason is described as follows. For
example, a film is formed on the surface of the defect such as a
foreign material in a film formation process or the like, resulting
in an increase in the size of the defect. This improves inspection
sensitivity. As a result, a defect present before the film
formation process is inspected after the film formation process.
More specifically, the defect present before the film formation
process is not inspected before the film formation process and is
inspected after the film formation process, resulting in the fact
that it is mistakenly determined that the defect occurs in the film
formation process.
In the defect inspection system according to the present invention,
however, the oblique detection optics system can be installed at a
position corresponding to a low elevation angle and is capable of
detecting only a defect present on the surface of the sample with a
reduction in the amount of light scattered from a background
defect. This makes it possible to eliminate an incorrect
determination.
As described above, the defect inspection system according to the
present invention is capable of improving the efficiency of
illumination. Also, the defect inspection system is capable of
detecting, with high sensitivity, a foreign material present on the
surface such as a LSI pattern by using the space filter and
optimizing the angle of the traveling direction of the illumination
light with respect to the surface of the sample. In addition, the
defect inspection system is capable of reducing light diffracted
from a pattern present on the substrate. Furthermore, the defect
inspection system is capable of setting a low detection threshold
for separating background light from light which is reflected on a
foreign material present on the surface of the sample and is
detected, in order to avoid an effect of an increase and reduction
in the amount of light due to thin film interference of diffracted
light caused by a variation in the thickness of the transparent
thin film.
Thus, the defect inspection system is capable of detecting a
microscopic foreign material present on the surface of the sample
having a length or diameter of about 0.1 .mu.m with high
sensitivity and preventing incorrect detection.
In the defect inspection system according to the present invention,
light scattered from a foreign material present on the surface of
the substrate and light scattered from an internal pattern can be
separated from each other. The defect inspection system performs
the inspection for each process for producing a wafer to determine
a process causing a foreign material, making it possible to quickly
identify a source of the defect.
In addition, the defect inspection system according to the present
invention is capable of simultaneously obtaining outputs from the
detector of the upward detection optics system and from the
detector of the oblique detection optics system in a single
inspection to obtain the double of the amount of information
compared with conventional techniques. This makes it possible to
reduce the throughput time by half.
Furthermore, the defect inspection system according to the present
invention has a plurality of the detectors capable of detecting
light scattered from a foreign material in a direction different
from that of light to be detected by the conventional techniques.
Since the defect inspection system can obtain the double of the
amount of information and the double of the value of the
information, the defect inspection system can determine the size
and the shape of the foreign material more accurately than the
conventional techniques.
It should be noted that, as shown in FIG. 7B, a plurality of the
adjusted elliptical lenses 10B can be installed in the same optical
axis thereof to correct aberration. In this case, when the
elevation angle is 12 degrees, seven to fifteen of the adjusted
elliptical lenses can be installed.
* * * * *